We are interested in studying the mechanisms which program the selective changes in gene expression during early embryonic development. Understanding the molecular events responsible for the heterogeneous cell-types arising from a single cell, the egg, is a fundamental unanswered question. Our approach to this problem is concerned with investigating during embryogenesis and in differentiated adult tissues the transcripts of a specific set of genes, those encoding the histone proteins. The histone proteins of sea urchins are encoded by several distinct sets of separately maintained multi-gene families that are expressed in a stage specific manner during embryogenesis and in differentiated adult tissues. Examples of these are the cleavage stage (CS) histones made only during oogenesis and the first three cleavages; the early histones made up until the blastula stage; the late histone subtypes which reach a maximum accumulation only at the gastrula; and adult tissue specific histones such as the sperm specific subtypes. The immediate objectives of the experiments outlined in this proposal are: 1) to clone and characterize the histone families not yet characterized (CS genes, most of the late genes, and the adult tissue specific genes); 2) to measure the absolute rates of transcription and decay of the late histone transcripts; 3) characterize the factors from sea urchin chromatin which exert biological effects on these genes. These studies pertain directly to understanding the evolution of multi-gene families and the role of differential gene expression in differentiation and embryogenesis. Our future goals include the utilization of transformation procedures to reintroduce altered forms of these genes back into the animal in the hopes of learning more about gene expression in embryos and what the role of the drastic alterations in chromatin structure during development might be.